A rack for electronic equipment, for example belonging to telecommunications systems, contains printed circuit boards on which are mounted electronic components and cables that connect said printed circuit boards to others, which may be situated in the same rack or in another, for example. The connection is effected in an interconnection unit, a backpanel.
A rack has at least a subrack on which are mounted the printed circuit boards, parallel to each other and perpendicular to the backpanel, since the latter is normally fixed to the rear part of the subrack in a plane perpendicular to the circuit boards. In summary, if the rack is viewed from the front, a front view of the backpanel is seen, while the view obtained of the printed circuit boards is an elevation.
The physical design of the rack is such that it permits assembly and disassembly of the printed circuit boards through its front part, since the racks normally have their back against another surface, such as for example a wall or the rear part of another rack, which does not permit access to the rack from the rear. In the same way, the cables for connecting the printed circuit boards of one rack with another rack, are also handled from the front side of the rack. Consequently, both the external cables and the printed circuit boards are connected and disconnected from the front part.
The backpanel comprises connectors to receive both the printed circuit boards and the cables that communicate with the exterior of the rack or with another subrack in the same rack.
To effect the electrical connection between the contacts of the different connectors, the backpanel is normally made up of various layers of printed circuit, on which the conductive tracks that connect electrically the contacts each other are laid.
The number of layers is a function of the number of electrical connections that have to be made, that is of the number of conductive tracks. Thus, to facilitate the layout of the tracks the connectors for the printed circuit boards are positioned in parallel on one sector of the backpanel, for example in the upper part, while in the other sector, the lower part, the cable connectors are mounted.
In summary, the connectors for printed circuit boards and for cables are normally aligned along a vertical axis, in this way maintenance personnel can easily identify the correspondence between cable and printed circuit board.
Nowadays, printed circuit boards are presenting higher levels of integration density, implying that more and more electronic components can be mounted on them, whereby their connectors have more contacts in order to communicate with the exterior.
As a result, a backpanel with the same number of connectors for printed circuit boards has to incorporate more connectors for cables and, consequently, to increase the number of tracks for connecting the contacts of board connectors with the board connectors, thus making necessary to increase the number of printed circuit layers that constitute the backpanel.
However, the backpanel cannot increase the number of layers indefinitely, since it would become unmanageable from the maintenance point of view. Moreover, as the number of layers increases, the cost rises rapidly.